[Ru(xantsil)(CO)(η6-toluene)]: Synthon for a Highly ... - ACS Publications

Feb 15, 2008 - Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101, Philippines. , §. The Open University of Japan, Chib...
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Organometallics 2008, 27, 918–926

[Ru(xantsil)(CO)(η6-toluene)]: Synthon for a Highly Unsaturated Ruthenium(II) Complex through Facile Dissociation of the Toluene Ligand [xantsil ) (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl)] Masaaki Okazaki,† Nobukazu Yamahira, Jim Josephus Gabrillo Minglana,‡ Takashi Komuro, Hiroshi Ogino,§ and Hiromi Tobita* Department of Chemistry, Graduate School of Science, Tohoku UniVersity, Sendai 980-8578, Japan ReceiVed NoVember 28, 2007

The reactions of [Ru(xantsil)(CO)(η6-C6H5CH3)] [1a, xantsil ) (9,9-dimethylxanthene-4,5-diyl)bis(dimethylsilyl))] with some electron-donating molecules were reported. When 1a was dissolved in benzene, benzene replaced the η6-toluene ligand easily at room temperature to give [Ru(xantsil)(CO)(η6-C6H6)] (1b). The η6-toluene ligand was also substituted by sterically less demanding two-electron donors smoothly at room temperature to afford [Ru(xantsil)(CO)L3] (L ) CH3CN (2), tBuNC (3), and PMe3 (4)). The X-ray diffraction studies revealed that they take a typical octahedral geometry, in which the xantsil ligand is coordinated to the Ru(II) center in κ2(Si,Si) fashion. Reactions of 1a with sterically demanding phosphines gave [Ru(xantsil)(CO)(PR3)] (R ) iPr (5) and Cy (6)). According to the X-ray diffraction study, complex 6 takes a square-pyramidal geometry, in which the xantsil ligand is bound to the Ru(II) center in κ3(Si,Si,O) fashion and one of the silyl groups occupies the apical position. The coordinatively unsaturated Ru(II) center is slightly stabilized by the agostic interaction by the C-H bonds in PCy3 [Ru · · · H: 2.89 and 3.06 Å]. The highly coordinatively unsaturated nature in 6 was indicated by the reaction with carbon monoxide molecules to give [Ru(xantsil)(CO)3(PCy3)] (7) at room temperature. The typical octahedral geometry with the κ2(Si,Si)-xantsil ligand was established by the X-ray diffraction study. Introduction Highly coordinatively unsaturated transition-metal complexes possessing 14 valence electrons are recognized as key intermediates in the homogeneous catalytic or stoichiometric reactions. In most of the reactions, the intermediates derived from oxidative addition or binding of substrates should leave adequate coordination vacancies, allowing further transformation reactions.1 The η6-arene-coordinated complex could be a promising candidate for such a species through the dissociation of the arene ligand. Thus, the exchange of arene molecules between free and bound states has been an important class of reactions in organometallic and surface chemistry. The arene exchange has been mechanistically investigated for late-transition-metal complexes.2 Several possible mechanisms have been reported so far. One mechanism involves an associative process as shown in Scheme 1. An initial rearrangement of the arene from η6- to η4-coordination occurs to give B. The incoming arene coordinates with B in η2-fashion to give C. Intramolecular rearrangement between two arene molecules, dissociation of the η2-arene

* Corresponding author. E-mail: [email protected]. † International Research Centre for Elements Science, Institute for Chemical Research, Kyoto University, Uji Kyoto, 611-0011, Japan. ‡ Institute of Chemistry, University of the Philippines, Diliman, Quezon City 1101, Philippines. § The Open University of Japan, Chiba, 261-8586, Japan. (1) Crabtree, R. H. In ActiVation and Functionalization of Methane; Davies, J. A. Ed.; VCH: New York, 1990; p 69. (2) (a) Muetterties, E. L.; Bleeke, J. R.; Sievert, A. C. J. Organomet. Chem. 1979, 178, 197. (b) Traylor, T. G.; Stewart, K. J.; Goldberg, M. J. J. Am. Chem.Soc. 1984, 106, 4445. (c) White, C.; Thompson, S. J.; Maitlis, P. M. J. Chem. Soc., Dalton Trans. 1977, 1654. (d) Green, M. L. H.; Joyner, D. S.; Wallis, J. M. J. Chem. Soc., Dalton Trans. 1987, 2823.

Scheme 1

molecule, and rearrangement of the resultant arene ligand from η4 to η6 give F. Taking into account the strong σ-donor and the trans-influencing ability of the silyl ligands,3 they are expected to exhibit an exceptionally strong trans effect. Therefore, silyl ancillary ligands would accelerate the dissociation of the η6-arene ligand to generate highly coordinatively unsaturated intermediates. Chelate formation often stabilizes the complex, and a series of (phosphinoalkyl)silyl ligands were demonstrated to work as supporting ligands and enabled reactivity studies on their complexes.4 Recently, we have developed a new type of bis(silyl) chelating ligand, (9,9(3) (a) Chatt, J.; Eaborn, C.; Ibekwe, S. Chem. Commun. 1966, 700. (b) Chatt, J.; Eaborn, C.; Ibekwe, S. D.; Kapoor, P. N. J. Chem. Soc. A 1970, 1343. (c) Bentham, J. E.; Cradock, S.; Ebsworth, E. A. V. J. Chem. Soc. A 1971, 587. (d) McWeeny, R.; Mason, R.; Towl, A. D. C. Discuss. Faraday Soc. 1969, 47, 20. (e) Mason, R.; Towl, A. D. C. J. Chem. Soc. A 1970, 1601. (f) Hartley, F. R. Chem. Soc. ReV. 1973, 2, 163. (g) Haszeldine, R. N.; Parish, R. V.; Setchfield, J. H. J. Organomet. Chem. 1973, 57, 279. (h) Yamashita, H.; Hayashi, T.; Kobayashi, T.; Tanaka, M.; Goto, M. J. Am. Chem. Soc. 1988, 110, 4417. (i) Lichtenberger, D. L.; Rai-Chaudhuri, A. J. Am. Chem. Soc. 1991, 113, 2923. (j) Levy, C. J.; Puddephatt, R. J.; Vittal, J. J. Organometallics 1994, 13, 1559.

10.1021/om701194e CCC: $40.75  2008 American Chemical Society Publication on Web 02/15/2008

[Ru(xantsil)(CO)(η6-toluene)]

Organometallics, Vol. 27, No. 5, 2008 919 Scheme 2

dimethylxanthene-4,5-diyl)bis(dimethylsilyl), or “xantsil”.5 In the last few decades, van Leeuwen et al. explored several diphosphine ligands having a xanthene or xanthene-like backbone and demonstrated their excellent effect on metal-catalyzed reactions based on their unique rigidity and large bite angle.6 We applied this rigid backbone, aiming at stabilizing the bis(silyl) chelate complexes, which are easily subjected to reductive elimination, nucleophilic substitution, insertion, and so on. Another characteristic feature of xantsil is the existence of the oxygen atom, capable of coordinating to the transition metal. In the substitution reactions of the η6-arene ligand with a two-electron donor, the intramolecular coordination of the xanthene oxygen atom would lower the activation barrier and stabilize the intermediate (Scheme 2). We report here the extremely accelerated η6-arene substitution reactions on the [Ru(xantsil)(CO)] fragment. Structures and properties of the resulting ruthenium(II) complexes, [Ru(xantsil)(CO)Ln] [Ln ) η6-benzene, (CH3CN)3, (tBuNC)3, (PMe3)3, PiPr3, PCy3, (CO)2(PCy3)], will also be discussed. Some of the results reported here have appeared elsewhere in a preliminary form.5a,d

Results and Discussion Facile Arene Exchange in [Ru(xantsil)(CO)(η6-C6H5CH3)] (1a). Extremely facile arene exchange was observed at room temperature in [Ru(xantsil)(CO)(η6-C6H5CH3)] (1a) when crystals of 1a were dissolved in benzene to give [Ru(xantsil)(CO)(η6C6H6)] (1b) quantitatively (eq 1). NMR data of 1b closely resemble those of 1a except for the data of the η6-benzene ligand. The 1H and 13C NMR signals of the η6-benzene ligand in cyclohexane-d12 were observed at δ 4.98 and 97.2, respectively. The high-field shift of the signals compared to free (4) (a) Stobart, S. R.; Zhou, X.; Cea-Olivares, R.; Toscano, A. Organometallics 2001, 20, 4766. (b) Brost, R. D.; Bruce, G. C.; Joslin, F. L.; Stobart, S. R. Organometallics 1997, 16, 5669, and references therein. (c) Okazaki, M.; Tobita, H.; Ogino, H. Organometallics 1996, 15, 2790. (d) Okazaki, M.; Tobita, H.; Ogino, H. Chem. Lett. 1997, 437. (e) Okazaki, M.; Tobita, H.; Ogino, H. J. Chem. Soc., Dalton Trans. 1997, 3531. (f) Okazaki, M.; Tobita, H.; Kawano, Y.; Inomata, S.; Ogino, H. J. Organomet. Chem. 1998, 553, 1. (g) Okazaki, M.; Ohshitanai, S.; Iwata, M.; Tobita, H.; Ogino, H. Coord. Chem. ReV. 2002, 226, 167. (5) (a) Tobita, H.; Hasegawa, K.; Minglana, J. J. G.; Luh, L.-S.; Okazaki, M.; Ogino, H. Organometallics 1999, 18, 2058. (b) Minglana, J. J. G.; Okazaki, M.; Tobita, H.; Ogino, H. Chem. Lett. 2002, 406. (c) Okazaki, M.; Minglana, J. J. G.; Yamahira, N.; Tobita, H.; Ogino, H. Can. J. Chem. 2003, 81, 1350. (d) Okazaki, M.; Yamahira, N.; Minglana, J. J. G.; Tobita, H. Organometallics 2004, 23, 4531. (e) Minglana; J. J. G.; Okazaki, M.; Hasegawa, K.; Luh, L.-S.; Yamahira, N.; Komuro, T.; Ogino, H.; Tobita, H. Organometallics 2007, 26, 5859. (6) (a) Kranenburg, M.; van der Burgt, Y. E. M.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. Organometallics 1995, 14, 3081. (b) Kranenburg, M.; Delis, J. G. P.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Vrieze, K.; Veldman, N.; Spek, A. L.; Goubitz, K.; Fraanje, J. J. Chem. Soc., Dalton Trans. 1997, 1839. (c) Buhling, A.; Kamer, C. J.; van Leeuwen, P. W. N. M.; Elgersma, J. W.; Goubitz, K.; Fraanje, J. Organometallics 1997, 16, 3027. (d) Kranenburg, M.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. Eur. J. Inorg. Chem. 1998, 155. (e) Goedheijt, M. S.; Reek, J. N. H.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. Chem. Commun. 1998, 2431. (f) Goertz, W.; Keim, W.; Vogt, D.; Englert, U.; Boele, M. D. K.; van der Veen, L. A.; Kamer, P. C. J.; van Leeuwen, P. W. N. M. J. Chem. Soc., Dalton Trans. 1998, 2981. (g) van der Veen, L. A.; Boele, M. D. K.; Bregman, F. R.; Kamer, P. C. J.; van Leeuwen, P. W. N. M.; Goubitz, K.; Fraanje, J.; Schenk, H.; Bo, C. J. Am. Chem. Soc. 1998, 120, 11616.

benzene is characteristic of the η6-arene ligands coordinated to transition metals. When the 1H NMR spectrum of 1b was measured in benzene-d6, the signal of the coordinated benzene diminished, showing fast exchange between the η6-benzene ligand and the benzene-d6 solvent. The arene exchange that occurs at room temperature is sill limited and has been reported for the nickel,7 iridium,8 and titanium9 systems. A series of nickel-arene complexes, [(C6F5)2Ni(η6-arene)], has been synthesized by a metal vapor synthetic method, in which the C6F5 group is essential for their isolation. The nickel-arene complexes reacted with electron-rich arenes, PEt3, 1,5-cycloocatadiene, and tetrahydrofuran to afford the substitution products at room temperature. Treatment of the dimer [Ir(µ-OMe)(cod)]2 with [HPiPr3](BF4) in acetone/benzene solution yielded the cationic arene complex [(η6-benzene)Ir(H)2(PiPr3)](BF4), of which the η6-benzene ligand was readily substituted with arenes in acetone through the transient formation of [(acetone)3Ir(H)2(PiPr3)](BF4). The reduction of TiCl4 in the presence of AlCl3 in benzene gave [(η6-C6H6)Ti(µ-Cl)4Al2Cl4], showing facile exchange with electron-rich arenes. Although π-arene complexes of group 8 transition metals have been of considerable interest over the last few decades, due to their high stoichiometric and catalytic activity,10 little is known about them possessing labile π-arene ligands. Complex 1 represents the first example of a ruthenium complex that undergoes arene exchange at room temperature.

(1) Substitution Reactions in [Ru(xantsil)(CO)(η6-C6H5CH3)] (1a) with Nitrile and Isonitrile. Crystals of 1a were dissolved in acetonitrile-d3, and the reaction was monitored by 1H NMR spectroscopy. Within 30 min at room temperature, the signals assignable to 1a diminished. Instead, the signals assignable to [Ru(xantsil)(CO)(CD3CN)3] (2-d9) and free toluene were observed in the appropriate region. A large-scale experiment using acetonitrile as a solvent allowed the isolation of [Ru(xantsil)(CO)(CH3CN)3] (2) as colorless crystals in 98% yield (7) (a) Klabunde, K. J.; Anderson, B. B.; Bader, M.; Radonovich, L. J. J. Am. Chem. Soc. 1978, 100, 1313. (b) Gastinger, R. G.; Anderson, B. B.; Klabunde, K. J. J. Am. Chem. Soc. 1989, 102, 4959. (8) (a) Torres, F.; Sola, E.; Martín, M.; López, J. A.; Lahoz, F. J.; Oro, L. A. J. Am. Chem. Soc. 1999, 121, 10632. (b) Torres, F.; Sola, E.; Martín, M.; Ochs, C.; Picazo, G.; López, J. A.; Lahoz, F. J.; Oro, L. A. Organometallics 2001, 20, 2716. (9) Pasynkiewicz, S.; Ciezyn´ski, R.; Dzierzgowski, S. J. Organomet. Chem. 1973, 54, 203. (10) (a) Bennett, M. A. In ComprehensiVe Organometallic Chemistry II; Abel, E. W., Stone, F. G., Wilkinson, G., Eds.; Pergamon: New York, 1995; Vol. 7, p 549. (b) Gimeno, J.; Cadierno, V.; Crochet, P. In ComprehensiVe Organometallic Chemistry III; Crabtree, R. H., Mingos, D. M. P., Eds.; Pergamon: New York, 2007; Vol. 6, p 531.

920 Organometallics, Vol. 27, No. 5, 2008 Scheme 3. Synthesis of [Ru(xantsil)(CO)L3] (L ) CH3CN (2), t BuNC (3))a

a (i) L ) CH3CN: acetonitrile, RT, 30 min; L ) tBuNC: + tBuNC, cyclohexane, RT, immediately.

Figure 1. ORTEP drawing of 2. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru-Si 2.3960(5), Ru-N1 2.2010(16), Ru-N2 2.119(2), Ru-C1 1.813(3), Si-Ru-Si* 96.17(2), C1-Ru-N1 101.28(7), C1-Ru-N2 170.73(9), N1-Ru-N2 85.50(5), N1-Ru-N1* 84.96(8), C1-Ru-Si 82.87(5), N2-Ru-Si 90.97(4), N1-Ru-Si 89.34(4), N1-Ru-Si* 173.51(4). Asterisks indicate atoms generated by the symmetry operation (x, -y + 1/2, z).

(Scheme 3). Elemental analysis established the formula of 2. The infrared (IR) spectrum shows three bands at 2362, 2336, and 1916 cm-1. The first two are assignable to the CN stretching vibration mode of three acetonitrile ligands. The last one is assignable to the CO stretching vibration mode, and the wavenumber is very close to that in 1a (1913 cm-1). The 29 Si{1H} NMR spectrum shows a singlet signal at δ 13.2, and the chemical shift lies in the typical range expected for silylruthenium(II) complexes.11 The molecular structure of 2 was determined by X-ray analysis (Figure 1). The molecule exhibits a mirror plane including Ru, O1, and C14 atoms. Complex 2 takes a slightly distorted octahedral geometry in which three incoming acetonitrile ligands occupy the fac-geometry, as suggested by the IR data. The interatomic distance of Ru-O1 is 3.563(2) Å, indicating no direct interaction between them. The Ru-Si bond distance [2.3960(5) Å] is within the range of those in related (11) (a) Eisen, M. S. In The Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y., Eds.; Wiley: New York, 1998; Vol. 2, Chapter 35, pp 2037–2128. (b) Tilley, T. D. In The Silicon-Heteroatom Bond; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1991; Chapters 9, 10, pp 245– 308, pp 309–364.

Okazaki et al.

silylruthenium(II) complexes. In general, both silyl and carbonyl ligands exhibit high trans influence, and the former is estimated to be higher than the latter. Accordingly, the bond distances of Ru-N1 and Ru-N1* (2.2010(16) Å) are significantly longer than that of Ru-N2 (2.119(2) Å), and both are considerably longer than the average Ru-N bond distances in acetonitrilecoordinated ruthenium complexes [2.05 Å]. The xanthene core is bent, and the dihedral angle between the least-squares planes of the two aromatic rings is 31.03(6)°. The toluene ligand in 1a was easily substituted by three t BuNC molecules in cyclohexane at room temperature to give [Ru(xantsil)(CO)(CNtBu)3] (3) in 82% yield [Scheme 3]. The 1H NMR spectrum of 3 shows two kinds of singlets for the CNtBu ligands at δ 0.44 (9H) and 1.02 (9H × 2). The former, located at the trans position of CO, appears at higher field probably due to the ring current of the xanthene arene rings. The signals for SiMe2 and 9,9-CMe2 are observed at δ 1.05 and 1.28 and δ 1.54 and 1.67, respectively. The 13C{1H} NMR signals can also be assigned in a similar way. The 29Si{1H} NMR spectrum shows a signal at δ -4.6, characteristic of the silyl-ruthenium(II) complexes. In the IR spectrum, in addition to the νCO band at 1927 cm-1, three strong-intensity bands of νCN are observed at 2127, 2137, and 2170 cm-1. The wavenumber is indicative of their linear coordination mode.12 Complex 3 is very stable in air even in solution, reflecting the rigid coordination of three isonitrile ligands to the Ru(II) center. A tentative X-ray structure analysis of 3 revealed the structure, in which three isonitirle ligands take a fac-geometry and one of them faces the xanthene core (see the Supporting Information). Substitution Reactions in [Ru(xantsil)(CO)(η6-C6H5CH3)] (1a) with Tertiary Phosphines. We examined the reactions of 1a with some tertiary phosphines. The η6-toluene ligand was substituted by three PMe3 molecules in dichloromethane at room temperature to give [Ru(xantsil)(PMe3)3(CO)] (4) in 84% yield (eq 2). The molecular structure of 4 was unequivocally determined by an X-ray diffraction study (Figure 2).5d Complex 4 takes a slightly distorted octahedral geometry, in which three incoming PMe3 ligands occupy the fac-positions. In contrast to 2 and 3, the carbonyl ligand faces the xanthene core to avoid the steric repulsion between the bulkier PMe3 and the xanthene moiety. The ruthenium-silicon bonds [Ru-Si1 (2.5276(8) Å) and Ru-Si2 (2.5234(8) Å)] are unusually long, which can be explained by the steric requirement of the xantsil ligand, which is enhanced by three bulky PMe3 ligands: That is, the rigid xanthene core forces two methyl groups (C3 and C4) to be within an extremely short interatomic distance (3.224(6) Å) compared to the sum of the effective van der Waals radii of two methyl groups (4.0 Å). The steric repulsion causes the other methyl groups (C2 and C5) on the silicon atoms to move closer to the methyl groups on the P2 and P3 phosphines (C2 · · · C25 3.250(5) Å, C5 · · · C28 3.298(5) Å), leading to considerable stretching of the ruthenium-silicon bonds. The high trans effect of the xantsil ligand and steric repulsion between the xantsil and PMe3 ligands mentioned above are reflected in the extremely high lability of the PMe3 ligands (eq 3). Even in a poorly coordinating solvent such as dichloromethane, an equilibrium is achieved instantaneously between 4 and 4′ through the dissociation of one of the PMe3 ligands. This is supported by the observation that when colorless crystals of 4 were dissolved in CD2Cl2, the solution turned yellow and the 1H NMR spectrum exhibited several signals assignable to (12) Cotton, E. A.; Wilkinson, G. In AdVanced Inorganic Chemistry, 5th ed.; Wiley: New York, 1988; p 256.

[Ru(xantsil)(CO)(η6-toluene)]

Organometallics, Vol. 27, No. 5, 2008 921

Figure 2. ORTEP drawing of 4. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru-P1 2.4004(8), Ru-P2 2.4003(8), Ru-P3 2.3930(8), Ru-Si1 2.5276(8), Ru-Si2 2.5234(8), Ru-C1 1.864(3), P1-Ru-P2 93.80(3), P2-Ru-P3 97.14(3), P3-Ru-P1 93.37(3), P1-Ru-Si1 92.31(3), P1-Ru–Si2 91.51(3), P2-Ru-Si1 85.09(3), P2-Ru-Si2 173.54(3), P3-Ru-Si1 173.74(3), P3-Ru-Si2 86.22(3), Si1-Ru-Si2 91.02(3), C1-Ru-P1 174.88(9), C1-Ru-P2 90.12(9), C1-Ru-P3 89.41(9), C1-Ru-Si1 84.73(8), C1-Ru-Si2 84.38(9).

on the potential energy surface. Dissociation of a PMe3 ligand located at the trans position of the silyl groups would be accelerated by their strong trans effect, giving 4a. Thus, 4a takes a square-pyramidal geometry with the silyl group (Si1) in the apical position. Isomerization between the pentacoordinated 4a and 4b seems facile. Subsequent intramolecular coordination of the xanthene oxygen atom gives 4c with 18 valence electrons. The interatomic distance of Ru-O1 (2.300 Å) in 4c is significantly shorter than those in 4a (3.671 Å) and 4b (3.351 Å) and lies in the range expected for the Ru-O dative bonds. Complex 4c is lowest in energy among three optimized forms. The geometry with two chemically inequivalent PMe3 ligands is consistent with the 31P{1H} NMR spectroscopic data. In the dissociation of the PMe3 ligand, coordination of the intramolecular oxygen atom in xantsil would be crucial to lower the activation barrier and stabilize the intermediate. The reaction of 1a with 5 equiv of PiPr3 in dichloromethaned2 was monitored by NMR spectroscopy (eq 4). After 10 min at room temperature, an equilibrium was attained between 1a, [Ru(xantsil)(CO)(PiPr3)] (5), toluene, and PiPr3 through the dissociation of the η6-toluene ligand, followed by the intramolecular coordination of the xanthene oxygen atom (vide infra). The molar ratio of 1a and 5 was estimated to be 1.0:1.6 based on the intensity of the 1H NMR signals. Addition of 20 equiv of PiPr3 shifted the equilibrium to the right side (1a:5 ) 1.0:9.1), although isolation of 5 was not achieved due to instability. Complex 5 was uniquely characterized by comparison of the NMR data with 6 (vide infra).

(4)

(2) resonances of 4′ and a broad signal of free PMe3 in addition to the signals of 4. No signal was observed in the high-field region characteristic of the Ru-H moiety. In the 31P{1H} NMR spectrum, three new broad signals were observed at δ -59.4, -6.5, and 27.4. The first signal was assigned to the dissociated PMe3, while the last two were assigned to 4′. Furthermore, addition of excess PMe3 to the yellow solution shifted the equilibrium in eq 3 to the left to form 4 predominantly, causing the yellow color to disappear. These results are consistent with the formula of 4′ as [Ru(xantsil)(CO)(PMe3)2].

Treatment of 1a with a bulkier PCy3 (5 equiv) gave [Ru(xantsil)(CO)(PCy3)] (6) in 76% yield (eq 5). The molecular structure was fully characterized by an X-ray diffraction study and consistent with the prediction by the DFT calculations (Figure 4).5d A characteristic feature of 6 is the intramolecular coordination of the oxygen atom in xantsil. The Ru-O1 distance of 2.268(4) Å is within the range expected for the ruthenium(II)oxygen dative bonds and close to that in [Ru{κ2(Si,Si)SiMe2O(Me)SiMe2}(H){κ3(Si,Si,O)-xantsil)}(CO)] [2.289(8) Å].5c Thus, complex 6 takes a distorted square-pyramidal geometry with the strongly electron-releasing silyl group of xantsil (Si1) in the apical position. The coordinatively unsaturated ruthenium center is stabilized by a weak agostic interaction of the C-H bonds in the cyclohexyl group [Ru-H15 ) 2.89 Å, Ru-H22 ) 3.06 Å] (Figure 5).

(3) To clarify the geometry of 4′, the geometry of [Ru(xantsil)(CO)(PMe3)2] was optimized by DFT calculations (Figure 3, Table 2). Three intermediates were identified as stationary points

(5) In the 1H NMR spectrum, four signals due to methyl groups appear at δ 0.20 (6H, SiMe), 0.51 (6H, SiMe), 1.51 (3H,

922 Organometallics, Vol. 27, No. 5, 2008

Okazaki et al.

Figure 3. Optimized structures of [Ru(xantsil)(PMe3)2(CO)] by the DFT calculation (B3LYP) with the use of a basis set, i.e., SDD for Ru, 6-31G(d) for Si and P, and 6-31G for the rest. Table 1. Crystallographic Data of 2 · CH3CN, 4, 6, 8 · CH2Cl2, and 9 formula cryst size (mm) fw cryst syst space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z F000 µ(Mo KR) (mm-1) no. of reflns collected no. of indep reflns (Rint) max. and min. transmn absorp corr no. of data/restrains/params R1, wR2 [I > 2σ(I)] R1, wR2 [all data] GOF largest diff peak and hole (e Å-3)

2 · CH3CN

4

6

8 · CH2Cl2

9

C22H30N4ORuSi2 0.40 × 0.40 × 0.10 617.86 orthorhombic Pnma 22.3683(7) 14.0012(3) 9.5533(2) 90 90 90 2991.93(13) 4 1280 0.635 21 810 3355 (0.0301) 0.94 and 0.79 numerical 3353/0/194 0.0273, 0.0653 0.0287, 0.0660 1.195 0.439 and -0.549

C29H51O2P3RuSi2 0.25 × 0.20 × 0.20 681.86 orthorhombic Pbca 17.0553(4) 20.1437(6) 19.2039(6) 90 90 90 6597.6(3) 8 2864 0.718 47 454 7552 (0.0525) 0.93 and 0.84 numerical 7552/0/349 0.0415, 0.1011 0.0525, 0.1280 1.226 0.625 and -1.1015

C38H57O2PRuSi2 0.10 × 0.10 × 0.05 734.06 triclinic P1j 10.1305(17) 10.3795(12) 19.2411(18) 98.116(4) 92.896(6) 112.966(8) 1831.7(4) 2 776 0.569 16 127 8050 (0.0551) 0.95 and 0.95 empirical 8050/0/403 0.0594, 0.1702 0.0830, 0.2028 1.165 0.888 and -1.831

C41H59Cl2O4PRuSi2 0.25 × 0.20 × 0.10 875.00 monoclinic P21/c 15.9513(5) 10.5822(3) 25.8317(10) 90 101.3523(10) 90 4275.1(2) 4 1832 0.624 31 960 9549 (0.0369) 0.94 and 0.86 numerical 9549/0/466 0.0420, 0.1350 0.0520, 0.1698 1.174 1.618 and -2.425

C40H48O4Ru2Si4 0.30 × 0.10 × 0.10 907.28 triclinic P1j 10.3381(4) 10.4244(6) 10.4263(5) 93.4825(14) 115.9243(10) 109.649(3) 922.65(8) 1 464 0.991 8263 4155 (0.0609) 0.91 and 0.76 numerical 4155/0/232 0.0420, 0.1175 0.0491, 0.1265 1.155 0.813 and -0.807

9-CMe), and 1.80 (3H, 9-CMe). No signals were observed in the high-field region typical for the metal-hydrido moiety. The 29 Si{1H} NMR spectrum exhibits only a doublet signal at δ 48.6 coupled with one 31P nuclei (JSiP ) 39.0 Hz). These spectroscopic features can be explained by assuming facile flipping of the PCy3 ligand as illustrated in Scheme 4. Kira et al. observed the related dynamic behavior of [(Cy3P)Pd{(R3Si)2SidSi(SiR3)2}] and estimated the symmetrical (Y-type) transition state for the flipping.13 The 31P{1H} NMR spectrum shows a signal at δ 25.0. The IR spectrum includes a strong bond at 1876 cm-1 assigined to the νCO band. Complex 6 can be a good synthon for the facile generation of a coordinatively unsaturated ruthenium(II) complex bearing 14 valence electrons through dissociation of the xanthene oxygen atom.14 The coordinative unsaturation of 6 was indicated by the reaction with CO (Scheme 5). A dichloromethane solution of 6 was stirred at room temperature for 1 h under a CO (13) Kira, M.; Sekiguchi, Y.; Iwamoto, T.; Kabuto, C. J. Am. Chem. Soc. 2004, 126, 12778.

atmosphere. Workup of the reaction mixture gave a white solid of [Ru(xantsil)(CO)3(PCy3)] (8) in 84% yield. Recrystallization from CH2Cl2/hexane gave colorless crystals of 8 suitable for X-ray diffraction study (Figure 6).5d Complex 8 adopts a slightly distorted octahedral geometry in which three carbonyl ligands are located in a mer-relationship. Accordingly, the interatomic distance of Ru-O1 [3.581(2) Å] indicates no interaction between them. The variable-temperature NMR study on the CD2Cl2 solution of 8 clearly indicated the existence of fluxional behavior. At 230 K, the Si-Me groups on xantsil shows four signals, which (14) (a) Ogasawara, M.; Huang, D.; Streib, W. E.; Huffman, J. C.; Gallego-Planas, N.; Maseras, F.; Eisenstein, O.; Caulton, K. G. J. Am. Chem. Soc. 1997, 119, 8642. (b) Huang, D.; Streib, W. E.; Bollinger, J. C.; Caulton, K. G.; Winter, R. F.; Scheiring, T. J. Am. Chem. Soc. 1999, 121, 8087. (c) Baratta, W.; Herdtweck, E.; Rigo, P. Angew. Chem., Int. Ed. 1999, 38, 1629. (d) Carmona, D.; Vega, C.; Lahoz, F. J.; Atencio, R.; Oro, L. A.; Lamata, M. P.; Viguri, F.; SanJose, E. Organometallics 2000, 19, 2281. (e) Sanford, M. S.; Henling, L. M.; Day, M. W.; Grubbs, R. H. Angew. Chem., Int. Ed. 2000, 39, 3451. (f) Watson, L. A.; Ozerov, O. V.; Pink, M.; Caulton, K. G. J. Am. Chem. Soc. 2003, 125, 8426.

[Ru(xantsil)(CO)(η6-toluene)]

Figure 4. ORTEP drawing of 6. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru-C1 1.803(6), Ru-O1 2.268(4), Ru-Si1 2.2870(16), Ru-Si2 2.3584(16), Ru-P 2.4522(15), C1-Ru-O1 158.9(2), C1-Ru-Si1 87.8(2), O1-Ru-Si182.05(11),C1-Ru-Si283.0(2),O1-Ru-Si281.31(11), Si1-Ru-Si2 102.97(6), C1-Ru-P 103.7(2), O1-Ru-P 96.62(11), Si1-Ru-P 102.08(6), Si2-Ru-P 154.30(6).

is consistent with the X-ray crystal structure. On warming, the signals at δ 0.64 and 0.72 coalesce at 270 K [∆ν (at 230 K) ) 26.6 Hz], and those at δ 0.46 and 0.66 at 286 K [∆ν (230 K) ) 61.1 Hz]. Finally, they become two singlet signals at room temperature. From the data, the barriers for two exchange process of Si-Me groups were calculated by the coalescence point method to be ∆Gq270 ) 57.7 kJ mol-1 and ∆Gq286 ) 56.2 kJ mol-1, respectively. A likely process is the inversion of the puckered chelate ring (Scheme 6). Such a fluxional behavior was also observed in 1, and the activation barrier of ∆Gq240 ) 47 kJ mol-1 was almost the same as that in 8. The 31P{1H} NMR spectrum shows a singlet signal at δ 39.3. The 29Si{1H} NMR spectrum at 230 K exhibits two doublet signals at δ -6.2 (JPSi ) 45.1 Hz) and -2.2 (JPSi ) 8.8 Hz), where the former is assigned to the silicon atom trans to PCy3 and the latter to that trans to CO based on the coupling constants of JPSi. The IR spectrum in CD2Cl2 contains three strong-intensity bands at 2040, 1992, and 1946 cm-1, characteristic of the mer-relationship of three carbonyl ligands. The reaction of 6 with CO was monitored spectroscopically (Scheme 5). Introduction of CO gas into an NMR tube containing the CD2Cl2 solution of 6 at room temperature caused the solution to turn from orange to dark green and then finally colorless. Accordingly, the 31P{1H} NMR spectrum indicated the existence of the intermediate 7 (δ 37.6), which was subsequently converted to the single product 8 (δ 39.3). The trans geometry of two carbonyl ligands in 7 is clearly supported by the IR spectrum: The intensity of the symmetric vibration

Organometallics, Vol. 27, No. 5, 2008 923

Figure 5. Agostic interactions between the Ru(II) center and cyclohexyl groups on PCy3. Scheme 4. Flipping of PCy3 on the Ru(xantsil)(CO) Fragment

Scheme 5

at 2036 cm-1 is quite weak, while that of the asymmetric vibration at 1927 cm-1 is strong. In the 29Si{1H} NMR spectrum, except the signals for 6 and 8, a new doublet signal was observed at δ 21.8 coupled with the 31P nuclei (2JPSi ) 23.2 Hz) that was attributable to 7. On the basis of these spectroscopic data, complex 7 is likely to take a squarepyramidal geometry with the silyl group in the axial position, which exhibits dynamic behavior including flipping of the PCy3 ligand as in 6. Thermolysis of [Ru(xantsil)(CO)(η6-C6H5CH3)] (1a) in the Absence of Donor Molecules. When 1a was heated in n-decane at 140 °C for 1 day in the absence of donor molecules, the dimer [Ru(xantsil)(CO)]2 (9) was obtained as yellow crystals in 73% yield. No NMR spectroscopic data were obtained for 9 due to its poor solubility in organic solvents. A strong band at 1917 cm-1 in the IR spectrum confirms the presence of CO,

924 Organometallics, Vol. 27, No. 5, 2008

Figure 6. ORTEP drawing of 8. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru-C1 1.934(4), Ru-C2 1.913(4), Ru-C3 1.928(4), Ru-P 2.4935(8), Ru-Si1 2.5366(9), Ru-Si2 2.5730(9), C1-Ru-C2 159.89(14), C1-Ru-C3 95.72(15), C2-Ru-C3 99.33(15), C1-Ru-P 96.25(10), C2-Ru-P1 97.90(10), C3-Ru-P 86.53(10), C1-Ru-Si1 85.88(10), C2-Ru-Si1 83.27(10), C3-Ru-Si1 81.43(10), C1Ru-Si2 83.99(10), C2-Ru-Si2 80.05(10), C3-Ru-Si2 175.93(11), P-Ru-Si1 167.93(3), P-Ru-Si2 97.54(3), Si1-Ru-Si2 94.50(3).

Okazaki et al.

Figure 7. ORTEP drawing of 9. Thermal ellipsoids are drawn at the 50% probability level, and hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ru-C1 1.818(4), Ru-C12 2.392(3), Ru-C13 2.288(4), Ru-C14 2.272(4), Ru-C15 2.251(3), Ru-C16* 2.415(3), Ru-C17 2.458(3), Ru-Si1 2.4392(10), Ru-Si2 2.4321(10), C6-C7 1.399(5), C7-C8 1.394(6), C8-C9 1.391(6), C9-C10 1.392(5), C10-C11 1.384(5), C11-C6 1.393(5), C12-C13 1.417(5), C13-C14 1.422(5), C14-C15 1.407(5), C15-C16* 1.428(5), C16*-C17 1.403(5), C17-C12 1.416(5), C1-Ru-Si1 81.40(12), Si1-Ru-Si2 95.26(3), C1-Ru-Si2 79.49(12). Asterisks indicate atoms generated by the symmetry operation (-x, -y, -z).

Conclusion 6

Scheme 6. Inversion of the Puckered Xanthene Chelate Ring in 8

and the value is comparable to that in 1a (1913 cm-1). A weak peak of M+ was observed at m/z 908 in the mass spectrum (EI). The structure of 9 was unequivocally determined by an X-ray diffraction study (Figure 7). Complex 9 is proven to be a dimer in which one of the arene rings of xantsil is coordinated to the ruthenium atom in a η6-fashion. The structure is essentially the same as 1a except that a Ru(xantsil)(CO) moiety replaces the η6-toluene as the η6-coordinated ligand. The ruthenium atom is bound equivalently to the six carbon atoms of the xanthene arene rings. The aryl C-C bond lengths of the η6-coordinated xantsil moiety range from 1.403(5) to 1.428(5) Å, while the aryl C-C bond lengths in the noncoordinated moiety range from 1.384(5) to 1.399(5) Å. The Si1-Ru-Si2 angle of 95.26(3)° is almost the same as that in 1a [94.81(6) Å]. There is no direct interaction between the two ruthenium atoms (Ru-Ru* 4.794 Å).

The η -toluene ligand in [Ru(xantsil)(η6-toluene)(CO)] (1a) can be readily replaced with an arene or some two-electron donor ligands under mild conditions. The substitution products also exhibit high lability through dissociation of the incoming ligands. The exceptionally high lability in the xantsil-ruthenium(II) system is attributable to (i) strong trans effect of two silyl groups, (ii) steric requirement of the xantsil leading to the severe repulsion between the SiMe2 parts of xantsil and the outgoing ligands, and (iii) intramolecular coordination of the xantsil oxygen atom leading to stabilization of the transition state and/or intermediate. Considering the high lability of the η6-toluene ligand, complex 1a could become a synthetic equivalent of the Ru(II) species with 12 or 14 valence electrons depending on the coordination of the xanthene oxygen atom. Such a highly coordinatively unsaturated species is expected to show higher catalytic activity than the corresponding 16electron species due to the presence of two or three easily accessible, low-lying empty orbitals that can be used in the reactions involving successive binding of substrates, oxidative addition, σ-bond metathesis, migration, etc.

Experimental Section General Procedures. All manipulations were carried out under a dry nitrogen atmosphere. Hexane and benzene were distilled from sodium-benzophenone ketyl and dichloromethane and acetonitrile from calcium hydride immediately prior to use. Benzene-d6 and cyclohexane-d12 were dried over a potassium mirror and dichloromethane-d2 and acetonitrile-d3 over molecular sieves 3 and 4 Å,

[Ru(xantsil)(CO)(η6-toluene)] respectively. They were transferred into an NMR tube under vacuum. [Ru(xantsil)(CO)(η6-toluene)] (1a) was prepared according to the literature method.5a,e Other chemicals were purchased and used as received. Physical Measurements. NMR spectra were obtained at room temperature unless otherwise indicated on a Bruker ARX-300 or AV-300 spectrometer. 1H, 13C{1H}, and 29Si{1H} NMR spectra were recorded at 300, 75.5, and 59.6 MHz, respectively, and referenced to SiMe4. 31P{1H} NMR spectra were recorded at 121.5 MHz and referenced to 85% aqueous H3PO4. 29Si{1H} NMR spectra were obtained by a DEPT pulse sequence. IR spectra were recorded on a Horiba FT-730 spectrometer. Mass spectra were measured using a JEOL JMS-HX110 or Hitachi M2500S spectrometer. Reaction of [Ru(xantsil)(CO)(η6-toluene)] (1a) with Benzene. Colorless crystals of 1a (10.0 mg, 0.0183 mmol) were dissolved in benzene (5 mL). After stirring for 3 h at room temperature, the solution was evaporated to dryness to give an analytically pure sample of [Ru(xantsil)(CO)(η6-C6H6)] (1b) as a white powder. Yield: 9.7 mg (100%). Anal. Calcd for C26H30O2Si2Ru: C, 58.73; H, 5.69. Found: 58.56; H, 5.89. MS (FAB, m-nitrobenzyl alcohol): m/z 532 (M+, 22), 454 (M+ - benzene, 100). 1H NMR (300 MHz, C6D12): δ 0.57, 0.64 (s, 6H × 2, SiMe2), 1.39, 1.78 (s, 3H × 2, 9,9′-CMe2), 4.98 (s, 6H, η6-C6H6), 7.00–7.26 (m, 6H, xanthene). 13 C{1H} NMR (75.5 MHz, C6D12): δ 4.6, 9.8 (SiMe2), 22.8, 31.0 (9,9′-CMe2), 36.5 (9,9′-CMe2), 97.2 (η6-C6H6), 122.9, 124.1, 129.6, 134.1, 138.3, 159.0 (xanthene), 201.2 (CO). 29Si{1H} NMR (59.6 MHz, C6D12): δ 13.3. IR (KBr, cm-1): 1911vs (νCO). Reaction of [Ru(xantsil)(CO)(η6-toluene)] (1a) with CH3CN. A suspension of 1a (150 mg, 0.275 mmol) in acetonitrile (5 mL) was stirred at room temperature for 1 h. Removal of volatiles under vacuum gave a white solid of Ru(xantsil)(CO)(CH3CN)3 (2), which was washed by hexane and dried under vacuum. Yield: 155 mg (98%). Anal. Calcd for C26H33N3O2RuSi2 · CH3CN: C, 54.43; H, 5.87; N, 9.07. Found: C, 54.10; H, 5.93; N, 8.65. 1H NMR (300 MHz, CD3CN, RT): δ 0.407, 0.411 (s, 6H × 2, SiMe2), 1.39, 1.78 (s, 3H × 2, 9-CMe2), 7.03–7.27 (m, 6H, xanthene). 13C{1H} NMR (75.5 MHz, CD3CN, 260 K): δ 5.0, 5.1 (SiMe2), 22.7, 30.4 (9CMe2), 36.4 (9-CMe2), 123.0, 123.2, 131.2, 133.2, 138.7, 159.4 (xanthene), 206.0 (CO). 29Si{1H} NMR (59.6 MHz, CD3CN, 260 K): δ 13.2. IR (KBr, cm-1): 2362w (νCN), 2336w (νCN), 1916vs (νCO), 1389vs, 1254m, 1227s, 1198w, 1125w, 835m, 815m, 777m, 750w. Due to the high lability of acetonitrile ligands, their 1H and 13 C NMR signals were not assigned. Reaction of [Ru(xantsil)(CO)(η6-toluene)] (1a) with tBuNC. A Pyrex NMR tube was charged with 1a (20.0 mg, 0.0366 mmol), t BuNC (14.0 mg, 0.168 mmol), and C6D12 (0.4 mL), and the solution was deaerated by argon for 5 min. The reaction was monitored by 1H NMR spectroscopy. Signals of 1a were cleanly replaced with those of [Ru(xantsil)(CO)(CNtBu)3] (3) within 1 h. The solution was slowly concentrated under vacuum to give colorless crystals of 3. Yield: 21.0 mg (82%). Anal. Calcd for C35H51O2Si2N3Ru: C, 59.79; H, 7.31; N, 5.98. Found: C, 59.80; H, 7.28; N, 5.91. MS (EI, 70 eV): m/z 703 (M+, 5), 675 (M+ - CO, 37), 620 (M+ - CNtBu, 84), 593 (M+ - CO - CNtBu, 100). 1H NMR (300 MHz, C6D6): δ 0.44 (s, 9H, CNtBu trans to CO), 1.02 (s, 18H, CNtBu cis to CO), 1.05, 1.28 (s, 6H × 2, SiMe2), 1.54, 1.67 (s, 3H × 2, 9,9′-CMe2), 7.18–7.69 (m, 6H, xanthene). 13C{1H} NMR (121.5 MHz, C6D6): δ 7.0, 8.8 (SiMe2), 24.5, 30.4 (CNC(CH3)3), 29.8, 30.1 (CNC(CH3)3), 36.4, 55.6 (9,9′-CMe2), 55.3 (9,9′-CMe2), 122.9, 124.4, 131.0, 133.2, 139.7, 159.5 (xanthene), 151.1 (CNC(CH3)3), 205.4 (CO). Only one 13C NMR signal assignable to the CNtBu3 ligands was found probably due to accidental overlap of the second signal with other signals or its low intensity. Reaction of [Ru(xantsil)(CO)(η6-toluene)] (1a) with PMe3. A Pyrex tube (10 mm o.d.) was charged with 1a (20.0 mg, 0.0366

Organometallics, Vol. 27, No. 5, 2008 925 mmol), PMe3 (22.0 mg, 0.289 mmol), and CH2Cl2 (0.5 mL) and connected to a vacuum line. The reaction mixture immediately turned yellow accompanied by the formation of colorless crystals of [Ru(xantsil)(CO)(PMe3)3] (4). The tube was flame-sealed and opened in a glovebox. The mother liquor was decanted and stored at -35 °C to give more crystals of 4. The crystals were washed with hexane and dried under vacuum. Yield: 21.0 mg (84%). 1H and 31P NMR data were collected in the presence of free PMe3. 13 C and 29Si NMR spectral data could not be obtained due to the low solubility of 4 in organic solvents. Anal. Calcd for C29H51O2P3RuSi2: C, 51.08; H, 7.54. Found: C, 50.53; H, 7.40. MS (EI, 70 eV): m/z 530 (M+ - 2PMe3, 8), 502 (M+ - 2PMe3 CO, 17), 325 (100). 1H NMR (300 MHz, CD2Cl2): δ 0.53, 0.62 (s, 6H × 2, SiMe2), 1.31, 1.71 (s, 3H × 2, 9,9′-CMe2), 1.34 (br., 18H, 2PMe3 cis to CO), 1.47 (d, 9H, 2JPH ) 6.7 Hz, PMe3 trans to CO), 6.96–7.21 (m, 6H, xanthene). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ -19.5 (d, 2JPP ) 36.5 Hz, 2PMe3 cis to CO), -16.2 (t, 2JPP ) 36.5 Hz, PMe3 trans to CO). IR (KBr, cm-1): 1932vs (νCO). Behavior of 4 in CD2Cl2. A Pyrex NMR tube was charged with 4 (15 mg, 0.022 mmol), and CD2Cl2 (0.5 mL) was introduced into this tube under high vacuum by the trap-to-trap transfer technique. The colorless solution immediately turned yellow. The yellow solution displayed the 1H and 31P NMR signals of 4, [Ru(xantsil)(CO)(PMe3)2] (4′), and free PMe3. Equilibrium was achieved immediately between 4, 4′, and PMe3 at room temperature. The molar ratio of 4 to 4′ was estimated to be approximately 10:9 based on the intensity ratio of the 1H NMR signals. The NMR tube was opened in a glovebox. Addition of excess PMe3 into the tube resulted in the formation of a colorless solution containing a single product, 4. Data for 4′: 1H NMR (300 MHz, CD2Cl2): δ 0.53 (s, 3H × 4, SiMe2), 1.12 (br, 9H, PMe3), 1.23, 1.66 (s, 3H × 2, 9-CMe2), 1.44 (br, 9H, PMe3), 7.05 (m, 2H, xanthene), 7.20 (m, 2H, xanthene), 7.45 (m, 2H, xanthene). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ -6.5, 27.4 (br, PMe3). Reaction of [Ru(xantsil)(CO)(η6-toluene)] (1a) with PiPr3. A Pyrex NMR tube was charged with 1a (5.0 mg, 9.2 µmol) and PiPr3 (8.8 µL, 5 equiv), and dichloromethane-d2 (0.5 mL) was transferred into the tube under vacuum. The tube was flame-sealed. After 30 min at room temperature, the reaction attained equilibrium between 1a and [Ru(xantsil)(CO)(PiPr3)] (5) in the molar ratio of 1:1.7. Due to the extremely high lability of PiPr3 ligands, isolation of 5 was not achieved even in the presence of excess PiPr3. 1H NMR (300 MHz, CD2Cl2): δ 0.24, 0.52 (s, 6H × 2, SiMe2), 1.03 (dd, 3JHH ) 7.0 Hz, 3JHP ) 13.0 Hz, 18H, P(CHMe2)3), 1.44, 1.79 (s, 3H × 2, 9-CMe2), 2.18 (septet, 3JHH ) 7.0 Hz, 3H, P(CHMe2)3), 7.14–7.33 (m, 6H, xanthene). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 33.0. 29 Si{1H} NMR (59.6 MHz, CD2Cl2): 51.8 (d, 2JPSi ) 41.8 Hz). Reaction of [Ru(xantsil)(CO)(η6-toluene)] (1a) with PCy3. A dichloromethane solution (14 mL) of 1a (100 mg, 0.183 mmol) and PCy3 (257 mg, 0.916 mmol) was stirred at room temperature in a glovebox. The solution turned from yellow to orange and finally to reddish-orange. After stirring for 30 min, volatiles were removed under reduced pressure. The resulting reddish-orange solid of [Ru(xantsil)(CO)(PCy3)] (6) was washed with hexane three times to remove excess PCy3 and dried under vacuum. Yield: 102 mg (76%). Anal. Calcd for C38H57O2PRuSi2: C, 62.17; H, 7.83. Found: C, 61.76; H, 7.98. 1H NMR (300 MHz, CD2Cl2): δ 0.20, 0.51 (s, 6H × 2, SiMe2), 0.80–2.01 (m, 33H, PCy3), 1.51, 1.80 (s, 3H × 2, 9-CMe2), 7.14–7.36 (m, 6H, xanthene). 13C{1H} NMR (75.5 MHz, CD2Cl2): δ 5.44 (d, 2JPC ) 5.2 Hz, SiMe), 8.17 (d, 2JPC ) 5.2 Hz, SiMe), 23.6, 31.0 (9-CMe2), 26.4 (Cy), 27.8 (d, JPC ) 9.2 Hz, Cy), 30.7 (Cy), 35.6 (d, JPC ) 8.0 Hz, Cy), 37.6 (9-CMe2), 124.2, 125.7, 130.8, 135.7, 136.4, 161.8 (xanthene), 208.0 (d, 2JPC ) 3.5 Hz, CO). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 25.0. 29Si{1H} NMR (59.6 MHz, CD2Cl2): δ 48.6 (d, 2JPSi ) 39.0 Hz), IR (KBr, cm-1): 1876vs (νCO).

926 Organometallics, Vol. 27, No. 5, 2008 Monitoring the Reaction of [Ru(xantsil)(CO)(PCy3)] (6) with CO. A Pyrex NMR tube was charged with 6 (7.0 mg, 9.5 µmol) and dichloromethane (0.5 mL). The solution was treated with CO gas (350 µL, 1.6 equiv) via syringe at room temperature and vigorously stirred. The orange solution gradually turned dark green. According to the NMR spectroscopic data, the reaction mixture consists of 6, [Ru(xantsil)(CO)2(PCy3)] (7), and [Ru(xantsil)(CO)3(PCy3)] (8) in the molar ratio of 0.3:1.3:1.0. Due to contamination of 6 and 8, isolation of 7 was not achieved. Data for 7: 1H NMR (300 MHz, CD2Cl2): δ 0.43 (s, SiMe2). 31P NMR (121.5 MHz, CD2Cl2): 37.6. 29Si{1H} NMR (59.6 MHz, CD2Cl2): δ 21.8 (d, 2JPSi ) 23.2 Hz). IR (CD2Cl2, cm-1): 1927vs, 2036vw (νCO). Synthesis of [Ru(xantsil)(CO)3(PCy3)] (8). A Schlenk tube was charged with a solution of 6 (75 mg, 0.102 mmol) in CH2Cl2 (5 mL), placed in liquid N2, and evacuated. After filling the tube with CO, the solution was allowed to warm to room temperature and then stirred for 1 h. Volatiles were removed under reduced pressure. The resulting white solid of 8 was washed with hexane three times and dried under vacuum. Yield: 68 mg (84%). Anal. Calcd for C40H57O4PRuSi2: C, 60.81; H, 7.27. Found: C, 60.45; H, 7.45. 1H NMR (300 MHz, CD2Cl2, 230 K): δ 0.46, 0.64, 0.66, 0.72 (s, 3H × 4, SiMe2), 0.77–2.31 (m, 33H, Cy), 1.29, 1.71 (s, 3H × 2, 9-CMe2), 6.93–7.43 (m, 6H, xanthene). 13C{1H} NMR (75.5 MHz, CD2Cl2, 200 K): δ 4.84, 6.20, 7.81 (SiMe), 7.11 (d, JPC ) 4.2 Hz, SiMe), 13.5, 21.5, 22.2, 35.6 (Cy), 24.8–31.2 (m, Cy and 9-CMe2), 34.9 (9-CMe2), 40.8–41.5 (Cy), 121.7, 121.8, 123.2, 123.4, 130.2, 131.1, 131.3, 132.1, 132.9, 156.5, 156.7 (xanthene), 197.6, 203.8, 204.5 (br, CO). 31P{1H} NMR (121.5 MHz, CD2Cl2): δ 39.3. 29 Si{1H} NMR (59.6 MHz, CD2Cl2, 230 K): δ -6.2 (d, 2JPSi ) 45.1 Hz, Si trans to PCy3), -2.2 (d, 2JPSi ) 8.8 Hz, Si trans to CO). IR (KBr, cm-1): 2040vs, 1992vs, 1946vs (νCO). Thermolysis of [Ru(xantsil)(CO)(η6-C6H5CH3)] (1a) in nDecane. Complex 1a (10.0 mg, 0.0183 mmol) and n-decane (1.0 mL) were placed in a Pyrex tube, which was flame-sealed under high vacuum. The sample was heated at 140 °C in an oil bath for 1 day. Fine crystals precipitated and the solution became light brown in color. The tube was opened inside the glovebox, and the mother liquor was decanted. The yellow crystals of [Ru(xantsil)(CO)]2 (9) were washed with hexane and dried under vacuum. Yield: 6.0 mg (72%). Due to the poor solubility of 9 in organic solvents, no NMR data were available. No acceptable data for elemental analysis were obtained because 9 cannot be purified due to its poor solubility. IR (KBr, cm-1): 1913 (νCO). Mass (EI, 70 eV): m/z 908 (M+, 29), 396 (M+/2 - SiMe2, 23), 381 (M+/2 - SiMe2 - Me, 100). X-ray Crystal Structure Determination. Crystals of 2 · CH3CN, 4, 6, 8 · CH2Cl2, and 9 were mounted at the end of a glass fiber for analysis using a Rigaku RAXIS-RAPID imaging plate diffracto-

Okazaki et al. Table 2. Selected Interatomic Distances (Å) and Angles (deg) in 4a-c Ru-Si1 Ru-Si2 Ru-P1 Ru-P2 Ru-C1 Ru-O1 Si1-Ru-Si2 Si1-Ru-P1 Si1-Ru-P2 Si1-Ru-C1 Si2-Ru-P1 Si2-Ru-P2 Si2-Ru-C1 P1-Ru-P2 P1-Ru-C1 P2-Ru-C1 Si1-Ru-O1 Si2-Ru-O1 C1-Ru-O1 P2-Ru-O1

4a

4b

4c

2.396 2.498 2.437 2.457 1.857 3.671 98.2 98.6 96.2 89.5 160.7 93.0 83.5 94.6 87.1 173.7

2.592 2.471 2.492 2.256 1.890 3.351 98.9 90.0 91.1 175.0 159.2 91.1 108.1 108.1 88.3 98.2

2.512 2.455 2.482 2.282 1.900 2.300 97.8 91.4 92.0 172.0 164.8 93.3 76.4 98.6 86.1 95.9 83.1 78.7 96.1 164.6

meter with graphite-monochromated Mo KR radiation. Data were collected at 150 K to a maximum 2θ value of 55.0°. Empirical or numerical absorption correction was applied, and the data were corrected for Lorentz and polarization effects. The structure was solved by direct methods and refined by full matrix least-squares techniques on all F2 data (SHELXL-97).15 The non-hydrogen atoms were refined anisotropically, and hydrogen atoms were located on idealized positions and refined using a restricted riding model. Selected crystallographic data are listed in Table 1.

Acknowledgment. This work was supported by Grantsin-Aid for Scientific Research (Nos. 18064003 and 18350027) from the Ministry of Education, Culture, Sports, Science and Technology of Japan. Supporting Information Available: A preliminary X-ray structure analysis of 3 in PDF format. Crystallographic data in CIF format for 2 · CH3CN, 4, 6, 8 · CH2Cl2, and 9. These materials are available free of charge via the Internet at http://pubs.acs.org. OM701194E (15) (a) Sheldrick, G. M. SHELXS-97, Programs for Solving X-ray Crystal Structures; University of Göttingen, 1997. (b) Sheldrick, G. M. SHELXL-97, Programs for Refining X-ray Crystal Structures; University of Göttingen, 1997.